1. Field Of The Invention
The present invention relates to a diaphragm type fuel pump in which fuel is introduced and discharged in accordance with strokes of a diaphragm.
2. Description Of Related Art
A diaphragm type fuel pump has been used up to now in order to introduce fuel into a fuel injector from a fuel tank. In the fuel pump, a diaphragm is operated using pulsating pressure of an engine in order to introduce and discharge fuel. Depending on the type of engine, fuel discharge pressure can sometimes become too large. Therefore, there are some diaphragm type fuel pumps provided with a fuel pressure regulating mechanism.
Japanese Patent Laid-Open No. Hei 11-201043 discloses a diaphragm type fuel pump including a fuel pressure regulating mechanism. Referring to FIG. 9 of the accompanying drawing figures, a fuel pump 70 includes: a fuel intake chamber 71; a fuel discharge chamber 72; a pump chamber 73; a fuel intake path 74 for introducing fuel from a fuel tank (not shown) to the fuel intake chamber 71; and a fuel discharge path 75 for discharging fuel to a fuel injector and or the like (not shown). Further, a fuel pressure regulating mechanism 76 is provided in the fuel discharge chamber 72. A fuel return pipe 77 connects the fuel pressure regulating mechanism 76 and the fuel intake chamber 71. The pressure regulating mechanism 76 is positioned outside the fuel pump 70, and returns the fuel from the fuel discharge chamber 72 to the fuel intake chamber 71 via the fuel return pipe 77 whenever the fuel pressure in the fuel discharge chamber 72 exceeds a predetermined value.
FIGS. 10 and 11 show a diaphragm type fuel pump 80 including a fuel pressure regulating mechanism (i.e., constituted of spill valve 96 and spring 98) which is structurally different from the fuel pressure regulating mechanism 76 of the fuel pump 70 shown in FIG. 9. A body 81 of the fuel pump 80 includes a partition wall 82, which defines, together with a diaphragm 84, a fuel intake chamber 86 and a fuel discharge chamber 88. Fuel is introduced into the fuel intake chamber 86 via a fuel intake path 90, and is discharged from the fuel discharge chamber 88 via a fuel discharge path 92. A path 94 is formed in the partition wall 82 in order to connect the fuel intake chamber 86 and the fuel discharge chamber 88. A spill valve (ball valve) 96 and a spring 98 are provided in the fuel intake chamber 86 in order to open and close the path 94.
Further, a cylindrical guide 99 is provided in the fuel intake chamber 86 in order that the spill valve 96 and the spring 98 move in a predetermined axial direction. The fuel intake path 90, fuel discharge path 92, path 94 and cylindrical guide 99 are substantially coaxial. A valve seat 100 is positioned at one end of the path 94 which is formed in the partition wall 82 and opens to the fuel intake chamber 86.
When a pressure in the fuel discharge chamber 88 is equal or less than the predetermined value, the spill valve 96 is pushed by the spring 98, sits on the valve seat 100 and closes the path 94, so that no fuel is returned to the fuel intake chamber 86 from the fuel discharge chamber 88. Otherwise, the pressure larger than the predetermined value pushes the spill valve 96 toward the fuel intake chamber 86 against the spring 98 and the pressure in the fuel intake chamber 86, thereby opening the path 94. Therefore, the high pressure fuel in the fuel discharge chamber 88 is returned to the fuel intake chamber 86, thus regulating the pressure of the fuel discharged via the fuel discharge path 92.
In the fuel pump shown in FIG. 9, the fuel pressure regulating mechanism 76 is arranged further out than the outer diameter D of the pump chamber 73 (shown by a dashed circle), which means that the fuel pump 70 is enlarged and becomes heavy because of the pressure regulating mechanism 76, and there is a problem related to fitting of the fuel pump 70.
Further, the fuel pump 70 should be provided with a fuel return pipe 77 running over an exterior thereof, which would lead to an increase in the cost of the fuel pump 70 and a problem of fitting.
In the diaphragm type fuel pump 80 of FIGS. 10 and 11, the fuel pressure regulating mechanism constituted by the spill valve 96 and the spring 98 is housed in the fuel intake chamber 86, which is effective in making the fuel pump 80 compact.
However, this fuel pump seems to suffer from the following three problems.
(1) Since the valve seat 100 at the opening of the path 94 near the fuel intake chamber 86 is positioned behind the cylindrical guide 99, the valve seat 100 is far from the fuel intake path 90 in the body 81, which makes it difficult to perform surface treatment of the valve seat 100 and to check plane accuracy thereof.
(2) Both the fuel intake path 90 and the path 94 are linearly positioned with the spill valve 96 interposed therebetween. Fuel flowing through the fuel intake path 90 and fuel flowing through the path 94 may adversely affect the operation of the spill valve 96, or may interfere with each other.
(3) The spring 98 may become long depending upon a mounting structure, which would cause variations in the dimensions of the spring 98. This would lead to varying performances of the spring 98.
Because of the above-described problems with respect to the fuel pressure regulating mechanisms of the foregoing fuel pumps 70 and 80, it is difficult to have the fuel pumps 70 and 80 function as desired and assure reliable performance.
The invention is devised in order to overcome the foregoing problems of the related art, and provides a compact diaphragm type fuel pump whose performance is reliable.
In order to accomplish the foregoing objects of the present invention, a diaphragm type fuel pump is provided which comprises; a fuel intake chamber; a fuel discharge chamber; a pump body; a diaphragm; a pump chamber; a return path; and a pressure control mechanism. The pump body has a fuel intake path communicating with the fuel intake chamber and a fuel discharge path communicating with the fuel discharge chamber. The diaphragm is fixedly attached to the pump body via a bottom body. The pump chamber is defined by the diaphragm and the pump body and communicates with the fuel intake path and the fuel discharge path. The return path connects the fuel intake chamber and the fuel discharge chamber. The pressure control mechanism is for returning fuel from the fuel discharge chamber to the fuel intake chamber via the return path when pressure in the fuel discharge chamber exceeds a predetermined value. The return path is formed in the pump body. A cavity is formed between outer and inner parts of the pump body, communicates with the return path via one end thereof and with the fuel intake or discharge chamber via the other end thereof and perpendicularly extends to the diaphragm. The pressure regulating mechanism is housed in the cavity, and is positioned inside an outer diameter of the pump chamber.